'Paint burning' effect
You might be able to do it that way, but I think I would make use of microdisplacement for the model.
I would recommend a tutorial but I can't find anything recent on it right now.  I'll just give you a quick and dirty rundown of the settings you need.
Cycles render engine
I recommend experimental feature set

I created a cylinder and added some loop cuts just to even out the geometry that our subdivision modifier is going to add.

Add a subdivision modifier and set it to something fairly high.

We can choose to use Adaptive here, it's available if you checked Experimental.  You may want to use this for rendering if you run into memory problems.
Add a material and then go into the material settings to enable displacement.

This is a node group I threw together just to get a decent example for you; something with some bigger globs and fine crunchy detail.

You could use an ambient occlusion map to guide the discoloration.  There's a lot more you can do here, but hopefully this will give you a starting point.